The invention relates generally to optical sensors for sensing the combustion of an air-fuel mixture within a combustion chamber of an internal combustion engine, and, more particularly, to a sensor for providing an ignition onset signal to a closed-loop regulating apparatus for controlling the engine combustion process.
The onset and the course of the combustion process within the cylinders of an internal combustion engine are important in determining the behavior of the engine. In an externally-ignited internal combustion engines, ignition of the fule-air mixture within each cylinder is initiated by an ignition spark, whereas in self-ignited internal combustion engines, the ignition of the fuel-air mixture within each cylinder is initiated by the injection of fuel into the cylinder. In both types of engines, there is a brief delay between the initiation of the ignition spark or the fuel injection and the actual onset of combustion of the fuel-air mixture.
The actual onset of combustion within a combustion chamber of an internal combustion engine may be precisely sensed by an optical sensor device. However, until the present invention, an optical sensor device for providing an ignition onset signal indicating the actual onset of combustion has not been used in known closed-loop control systems for regulating the onset of combustion in accordance with selected operating parameters, such as engine speed, for the reason that prior known optical sensors for sensing conditions within the combustion chamber of an internal combustion engine generally are relatively expensive laboratory devices which are not designed for reliable operation over the normal operational life of the engine, at least not without requiring extensive maintainance at relatively frequent intervals. Consequently, until the present invention, sensors for indicating the initiation of either the ignition spark or the fuel injection which determines the onset of combustion have been used in these closed-loop control systems.
For example, U.S. Pat. No. 4,033,310, issued July 5, 1977 to Nicholls, U.S. Pat. No. 4,019,478, issued Apr. 26, 1977 to Hobo et al, U.S. Pat. No. 3,934,430, issued Jan. 27, 1976 to Fuso, and U.S. Pat. No. 3,796,197, issued Mar. 12, 1974 to Locher et al, incorporated herein by reference, describe closed-loop control systems in which the onset of fuel injection in a Diesel engine is regulated to thus regulate the onset of ignition. Each of these known regulating systems include a fuel injection onset sensor, engine operating parameter sensors, including an engine speed sensor, and an electronic controller which is connected to receive the output signals of these sensors. The electronic controller includes a signal processing circuit for generating a set-point corresponding to the desired fuel injection onset and a comparator circuit for comparing the set-point signal with the output signal of the fuel injection onset sensor to generate a deviation signal corresponding to the difference between the actual and desired fuel injection onset values. The deviation signal is supplied to a final control element of an injection adjuster for adjusting the fuel injection timing of a fuel injection timing of a fuel injection pump driven by the engine in accordance with the deviation signal to achieve the desired fuel injection onset. It would be highly desirable if these known closed-loop systems included an optical sensor for detecting the onset of ignition, rather than a sensor for detecting the onset of fuel injection, since it is the onset of ignition which determines the functioning of the engine.
U.S. Pat. No. 2,841,979, issued July 8, 1958 to Harbert, describes a device for observing combustion phenomena occurring within spark-ignited internal combustion engines. The device includes a spark plug having a hollow central electrode containing a rod formed of a transparent material such as quartz or sapphire, which transmits light impinging on the end of the transparent rod exposed to the combustion chamber through the rod and a heat exchanger for the spark plug to a photoelectric cell or the like, which generates a signal proportional to this light. It is indicated that the deposition of carbon or other material on the transparent rod is much less than the deposition of such materials on the surface of quartz windows, disposed in the engine block, which were previously used to observe combustion phenomena. Consequently, the length of test runs of a spark-ignited internal combustion engine, during which this device is used to observe combustion phenomena, is much greater than that previously possible using quartz windows, and runs over 100 hours in length have been conducted using this device with no problem of lack of light from the combustion reaction being encountered.